Typical Spinal Nerve

Sanjaya AdikariDepartment of Anatomy

Skull

Vertebral column

• CNS is covered

by the skull and

the vertebral

column

• PNS is outside

C N S P N S

N ervous sytem

C N S P N S

S o m a tic

C N S P N S

a u to n om ic

N e rvo us sytem

Structure of a spinal cord segment

Posterior median septum

Posterior horn

Lateral horn

Anterior horn

Anterior median fissure

Central canal

Posterior white column

Lateral white column

Anterior white column

Anterior nerve root

Posterior nerve root

Dorsal root ganglion

Somatic

Autonomic

Dorsal and ventral roots

• Dorsal roots contain afferent (sensory) axons

• Ventral roots contain efferent (motor) axons

• The ventral roots continue out from the spinal

cord, and mix with their corresponding dorsal

nerve root at a point after the ganglion

• The combined dorsal and ventral roots are

called a spinal nerve (therefore, spinal nerves

are mixed).

Spinal nerve is mixed (motor + sensory + autonomic)

Spinal nerve is mixed (motor + sensory + autonomic)

• Spinal nerve refers to the mixed spinal nerve

• It is formed from the dorsal and ventral roots

• Passes out through the intervertebral foramen

• There are 31 bilaterally-paired spinal nerves

– 8 cervical nerves (C1-C8)

– 12 thoracic nerves (T1-T12)

– 5 lumbar nerves (L1-L5)

– 5 sacral nerves (S1-S5)

– 1 coccygeal nerve (Co)

7

12

5

5

8

12

5

5

1

Vertebral column Spinal cord

C2

C1

C4

C3

C6

C5

T1

C7

T3

T2

T5

T4

T7

T6

T9

T8

T11

T10

L1

T12

C1

C8

T3

T10

L1, L2

L3, L4

L5

S, C

C1

C7

C8

Spinal nerves

T1

T2

T10

Anterior and posterior primary rami

• The posterior primary rami have lateral and medial branches

They supply

– back muscles and skin over the back

• The anterior primary rami give off anterior and lateral cutaneous branches

They supply

– the rest of the body wall

• Anterior primary rami also give rise to the roots of the various nervous plexuses

Spinal nerves in the thoracic region

Anterior cutaneous branch

Lateral cutaneous branch

Medial Lateral

Anterior

Posterior

These are typical spinal nerves

• Gray ramus communicans

unmyelinated

• White ramus communicans

myelinated

Rami communicantes

Formed by communicating

branches between anterior

primary rami of spinal nerves.

Anterior primary rami form the

roots of nerve plexus

What are the advantages of a nerve plexus?

Last’s Anatomy, 10th ed. Page 13

Nerve plexus

DermatomeArea of skin supplied by a single spinal nerve or spinal cord segment

Myotome

The muscle/s supplied by a single spinal nerve or spinal cord segment